The World Meteorological Organization said it is too soon to know whether intense heat waves sweeping Europe, parts of the United States and southern China are linked to climate change. The WMO said more investigation is needed to determine the cause of the phenomenon.

Millions of people throughout Europe are wilting under temperatures of more than 40 degrees Celsius, in some cases. The World Meteorological Organization warned no immediate respite from the extreme heat is in sight as many parts of Europe will continue to see extremely high temperatures and dry weather conditions over coming days.

WMO spokeswoman Claire Nullis said the current heat wave is unusual because it is so early in the season and so widespread.

“We are getting comparisons between this heat wave and the one in 2003, which was the big European heat wave, which killed tens of thousands of people in Europe," she said. "The difference is that the 2015 heat wave … is much earlier and Europe is much, much better prepared to cope with the impacts.”

While western, southern, and central Europe are suffering from this unusual heat wave, WMO said northern Europe is experiencing one of the coolest summers ever, with temperatures in Lapland running between 10-15 degrees Celsius.

WMO climate expert Omar Baddour said it is premature to link the European heat wave to climate change while it is still going on.

“We need to simulate through the computer to attribute what part is related to climate change and what part is related to natural climate variability and what will be the part linked to El Nino, which is still in its early stage," he said.

Baddour said this is a very difficult question, but that "it fits well with what climate change predicts of increasing frequency and intensity of heat waves.”

WMO’s weather map shows many parts of the western United States are suffering from high temperatures. The agency warned further drying of soil in the states of California, Washington and Oregon will increase the risk of wildfires. It said Canada also is gearing up for severe wildfires.

WMO noted heat waves in numerous other places around the world. This includes southwest China, which has temperatures of over 35 degrees Celsius along with very heavy rain, and southeast China, which is suffering from extreme heat.